First-principles Investigations Of Electronic Properties Of Two-dimensional Arsenene And Antimonene In Different Phases And The Phase Diagrams Of Nano-alloys

With the ultrafast development and investigation of nano-materials,the exploration in the world of nanometer is more deeply by means of the advanced experimental equipment and computational material science.Based on the size-dependent effect,nano-materials possess the remarkable physical and chemical properties which do not appear in the bulk.Therefore,nano-materials are worth to investigate widely in the material science.In this work,by using the first-principles,we studied two topics in this field.One is the modulation of the electronic properties in two-dimensional（2D）arsenene and antimonene,and another one is the novel method that could obtain the size-dependent phase diagrams of nano-alloys.1.As a new branch of nano-materials,2D material with excellent physical and chemical properties have received much attentions.2D materials in Group-V are no-zero band gap semiconductors and have diverse phase allotropes.The application in the electronic devices of phosphorene slowed down due to the low stability.However,arsenene and antimonene do not bother with this problem.At present,the studies of arsenene and antimonene mainly focus on the modulation of their indirect band gap and the interlayer interaction with other layered materials.Based on the reports presently,three aspects of this work are shown below:（1）The prediction of a new series of 2D materials,namely,arsenene and antimonene have enriched the field of nano-devices fabrication.However,the indirect band gap character of the pristine structures slows down the pace of their practical applications.Herein,we design and study novel monolayer AsxSby alloys with excellent stabilities（where x and y denote the atomic ratio of As and Sb elements and x+y=16）by using density functional theory（DFT）.The results indicate that some components possess direct band gaps.Moreover,the low effective masses（lower than 0.2m₀,where m₀ is the static electron mass）of the alloys are also obtained,which will enhanced the device efficiency.In particular,α-phase AsxSby（5<y<9）harbors the low effective masses even lower than phosphorene.Our predictions not only inject new vigor into 2D alloys,but also highlight the potential of these alloys as fascinating materials for future nano-electronic devices.（2）Group-V layered materials with semiconducting electronic properties are emerging as promising layered materials.Since the layered configurations need substrate for device fabrications,their surface energy values could decide their properties.Here,we perform a systematic investigation on the surface energies of arsenene and antimonene as the function of thickness by using DFT.The results show that the surface energy values ofβphase increase with increased layered numbers and converge to a constant value about five layers,while the surface energy values ofαphase are size-independent.The surface energy values of bothαandβphase are similar,which would ensure the existence ofαphase.All these could give references for the future manufacture of nano-devices based on arsenene and antimonene.（3）Arsenene-based devices such as transistors and photodetectors which benefit from the control of carrier type and concentration as well as the high quality p-or n-doped components in p-n junctions.In this work,the electronic properties of selective organic molecules adsorbed on S/O arsenene are investigated by using DFT.The results show that different doping types could be obtained by controlling the kinds of organic molecules.The doped arsenene still maintain the direct band gap and the gap values change a little.In TTF/As system,typical n-doped arise,while typical n-doped are shown in TCNE/As and F4-TCNQ/As.In both TTF/As and TCNE/As,the adsorption position has little influence on the band gap and ionization energy.Furthermore,small ionization energy appear in F4-TCNQ/As that carriers could be ionized easily,and this would enhance the amount of carriers.Therefore,p-n junction is expected to be prepared based on S/O phase arsenene by doping different organic molecules.2.The construction of temperature-composition phase diagrams of nano-alloys is critical to their industrial applications.However,phase diagrams of nano-alloys are difficult to be determined precisely by experiments which because that the nano-alloy is metastable mostly.In this work,a simple approach is developed to obtain continuous binary solution phase diagrams both bulk and size-dependent.First,determining bulk atomic interaction energy by using ab initio molecular dynamics simulation.Second,calculating the melting enthalpy,melting temperature,and atomic interaction energy which are size-dependent by using a unified nano-thermodynamics model.In the end,drawing the phase diagrams with the parameters in the previous step.A typical Au-Ag alloy is investigated in this work as an example.The calculated atomic interaction energy in bulk is corresponding to the experimental data,which demonstrate the credibility of the calculation methods.Furthermore,the melting enthalpy,melting temperature,and atomic interaction energy all decrease with the size decreasing.At the same time,the solidus and liquidus curves temperatures descend,and the area of two-phase zone change to small in nano-alloy.The general approach developed here can be used to investigate other continuous binary alloy systems and can be helpful in the preparation of nano-alloy.